1. Field of the Invention
This invention in the first aspect relates to a process for producing a high-stiffness polypropylene. More particularly it relates to a process for producing a high-stiffness polypropylene having a far superior transparency.
Further, this invention in the second aspect relates to a highly stereospecific polypropylene. More particularly it relates to a polypropylene affording a molded product having a far superior transparency, stiffness and durability according to a conventional molding process even without adding any particular additive, and a broad molecular weight distribution and a very high stereoregularity.
2. Description of the Related Art
The inventors of Chisso Corporation have previously proposed a process for producing a high-stiffness polypropylene using a catalyst prepared by combining a titanium trichloride composition obtained according to a specified process with an organoaluminum compound an aromatic carboxylic acid ester, each in specified proportions (Japanese patent application laid-open No. Sho 58-104,907, hereinafter referred to as the prior application invention). According to the process of this prior application invention, it has become possible to produce a polypropylene affording a molded product having a far higher stiffness than that of polypropylene obtained according to conventional known processes, even without adding any particular additive.
However, while the polypropylene obtained according to the prior application invention has the above-mentioned high stiffness, it is translucent and hence in the field of its use applications, the commodity value has often been damaged so that improvement in the transparency has been desired.
On the other hand, as an attempt of improving the transparency of polypropylene or as another attempt of improving the stiffness, various processes have been proposed such as those of polymerizing propylene using a catalyst subjected to a preliminary activation treatment by polymerizinq a small quantity of a non-linear olefin such as vinylcyclohexane, p-t-butylstyrene, allyltrimethylsilane, 4,4-dimethylpentene-1, etc., or a catalyst obtained by the preliminary activation treatment with a non-linear olefin, followed by a prelimiary activation treatment with propylene (Japanese patent application laid-open Nos. Sho 60-139,710, Sho 63-15,803, Sho 63-15,804, Sho 63-37,105, Sho 63-218,709, etc.). Thus, the present inventors have carried out polypropylene production according to these proposed processes. As a result, according to any of these processes, the polymerization activity of propylene not only lowers, but also operational problems occurred such as formation of massive polymer, adhesion of scales onto the wall of the polymerization vessel, inferior controllability of polymerization reaction, etc.; hence it was impossible to employ these processes in the case of commercial long term continuous polymerization processes, particularly in the case of gas phase polymerization process of carrying out propylene polymerization in gas phase.
Further, the stiffness of the resulting polypropylene was lower and insufficient as compared with that of polypropylene obtained according to the process of the prior application invention. Further, when the polypropylene was processed into film, a definite improvement in the transparency was observed, but a number of voids occurred in the film to damage its commodity value.
Further, as a similar technique, a process has been proposed wherein propylene is polymerized using a catalyst component obtained by adding a non-linear olefin polymer such as vinylcyclohexane polymer, allyltrimethylsilane polymer, etc., midway during the production of the transition metal component for propylene polymerization (Japanese patent application laid-open No. 63-69,809), but this proposed process requires a separate process of producing a non-linear olefin polymer so that the process has been not only accompanied with a commercial disadvantage, but also there have been raised problems of insufficient stiffness and occurrence of voids in the film as in the case of the above-mentioned prior art.
The present inventors have made extensive research on a process for producing a high-stiffness polypropylene having solved various problems of the above-mentioned prior application invention and prior art and having an improved transparency, and as a result, have found a titanium trichloride composition having a linear olefin-non-linear olefin block copolymer contained therein, and further have found that when this titanium trichloride composition is combined with specified quantities of an organoaluminum compound and further an aromatic carboxylic acid ester and polypropylene is produced using the resulting catalyst, then the problems of the above-mentioned prior art in the aspect of production and quality are dissolved and also the polypropylene has not only a far superior transparency, but also a further improved stiffness as compared with the polypropylene obtained according to the process of the prior application invention, and thus have completed the present invention in a first aspect.
As apparent from the foregoing, the object of the present invention in the first aspect is to provide a process for producing a high-stiffness polypropylene having very small occurrence of voids and a far superior transparency.
Further, the prior art related to the present invention in the second aspect and its problems will be described below.
Polypropylene are superior in the heat resistance, chemical resistance and electric properties and further are good in the stiffness, tensile strength, optical characteristics and workability; thus it has been broadly applied to injection molding, extrusion molding, blow molding, etc.
However, known conventional polypropylene has been restricted in its use applications due to the limits of physical properties and workability; hence in order to solve the above-problems, improvement in the properties of polypropylene, particularly improvements in retention of stiffness and strength at high temperatures, durability, moldability of large-size molded products, etc. have been earnestly desired.
As to the improvement in the above various properties, various attempts have been continued such as enhancing the stereoregularity of polypropylene to thereby improve physical properties such as heat resistance, stiffness, strength, etc., broadening the molecular weight distribution to thereby improve the strength and durability depending upon the high molecular weight part and thus improve the moldability at the time of extrusion molding, blow molding, etc.
The inventors of Chisso Corporation, too, have previously proposed a highly stereoregular polypropylene having a broad molecular weight distribution in Japanese patent application laid-open Nos. Sho 59-22,913 and Sho 63-191,809. By using this polypropylene, a molded product having a far higher stiffness and durability as compared with known conventional polypropylene has been obtained to thereby make it possible to broaden the fields of its definite use applications. However, while the boiling n-heptane-insolubles of the polypropylene have a high stereoregularity, the stereoregularity of the total polymer is insufficient and hence further improvement in the stereoregularity has been desired and besides, improvement in the transparency has also been desired.
Further, as to other techniques for providing polypropylene having a relatively high stereoregularity, for example the following polypropylenes have been disclosed:
polypropylene obtained by using a titanium trichloride composition as a solid catalyst component such as polypropylene obtained by using a catalyst having a titanium trichloride composition combined with an alkoxyaluminum compound and an ester compound (Japanese patent publication No. Sho 64-9,325), polypropylene obtained by subjecting a non-linear olefin such as 4-methylpentene-1 to preliminary polymerization using a catalyst consisting of a titanium trichloride composition and an organoaluminum compound, followed by polymerizing propylene (Japanese patent application laid-open No. Sho 61-155,404), polypropylene obtained by using a catalyst having a titanium trichloride composition combined with an organoaluminum compound, an organometal-intermolecular coordination compound and further an electron donor (Japanese patent application laid-open No. Sho 62-100,505), etc., polypropylene obtained by using a catalyst having the so-called supported type solid catalyst component obtained by having TiCl.sub.4 supported on a Mg compound combined with an organoaluminum compound and further an organosilicon compound (Japanese patent application laid-open No. Sho 58-83,006, Japanese patent application laid-open No. Sho 64-66,217), etc.
However, polypropylenes disclosed in the above Japanese patent publication No. Sho 64-9,325) and Japanese patent application laid-open No. Sho 62-100,505 have been insufficient in the stereoregularity as the whole of the polymer; hence the stiffness, heat resistance, etc. of molded products obtained by using the polypropylenes have been insufficient. Further, polypropylenes disclosed in Japanese patent application laid-open Nos. Sho 58-83,006, Sho 61-155,404 and Sho 64-6,621 have a stereoregularity to a definite extent, but since they have a narrow molecular weight distribution, their durability has been extremely insufficient. Further, the polypropylene disclosed in Japanese patent application laid-open No. Sho 61-155,404 has an improved transparency to a definite extent, but the improvement is still insufficient, and besides, the polypropylenes disclosed in Japanese patent publication No. Sho 64-9,325, Japanese patent application laid-open Nos. Sho 58-83,006, Sho 62-100,505 and Sho 64-6,621 are extremely insufficient in the transparency.
On the other hand, as a technique for providing a polypropylene having an improved transparency, a process of using a catalyst consisting of a titanium compound and an organoaluminum compound, using subjecting a non-linear olefin such as vinylcyclohexane, etc. to preliminary polymerization, followed by polymerizing propylene (Japanese patent application laid-open No. Sho 60-139,710) is mentioned. While the polypropylene obtained according to the process is observed to have an improved transparency to a definite extent, there has been raised a problem that the resulting polymer is uneven due to polymerization unstability caused by inferior shape of the catalyst component after the preliminary polymerization, and further, the stiffness and durability have been inferior due to insufficient stereoregularity and narrow molecular weight distribution.
In view of the present status of the above-mentioned prior art, the present inventors have made extensive research in order to find a polypropylene having a broad molecular weight distribution and an extremely high stereoregularity and affording a molded product having a notably superior transparency, stiffness and durability according to a conventional molding process, even without adding any particular additive, and as a result, we have found that when a novel polypropylene satisfying the requirements of the present invention, described below, is subjected to molding processing, then it is possible to obtain a molded product having a far superior transparency, stiffness and durability, and have completed the present invention in the second aspect.
As apparent from the foregoing, an object of the present invention in the second aspect is to provide a novel polypropylene capable of producing a molded product having a far superior transparency, stiffness and durability. Another object is to broaden the fields of concrete use applications.